The only thing that I could say about rough lumber would be to make sure
that as with any material ensure it is not too green or otherwise leave your
boxes oversize and cut them down after the material has shrunk however
amount its going to.  Also it would be preferable if the rough material were
bandsawn lumber as it will be more likely to maintain its dimension as
regards to thickness over the lenth of the boards.  Also it will be much
smoother and easier to work with.  As to the knots, I just keep a brush
handy as I'm cutting hand-holds and shellac them from the inside, or if the
knots have already fallen out a small piece of tin works well to make them
bee-tight.  Of course don't do this till after the hand-holds are cut though
and avoid possibly hitting a nail with the cutter. Other than that and the
difficulty in finishing the outside there should'nt be a problem.  If you
could get it planed for 100-150 dollars it might be worth it too just to
have that much nicer and smoother equipment to handle later on.  When you
handle a painted rough surface later on it is very abrasive and pokey.  It
would amount probably to about 1 dollar per box to have it planed.
Hope I've been a help.  Merry Christmas everyone.
 
Doug McCulloch